The present invention relates to a casting apparatus and more particularly to a casting apparatus for die casting machines which are capable of feeding molten metal efficiently into a vertically oriented injection sleeve for supplying the molten metal to a die casting chamber. The present invention reduces the problems associated with oxidation of the molten metal during the casting operation and ensures that accurate dosages of molten metal are delivered to the casting chamber at all times in order to yield high quality castings free of defects.
Casting apparatus have widely been used for obtaining a large quantity of desired cast products by supplying molten metal into a die cavity of a given shape and allowing the metal to solidify in the die cavity. Casting apparatus can roughly be classified as hot chamber and cold chamber casting apparatus.
One known type of cold chamber die casting machine is illustrated in FIG. 1 of the accompanying drawings. A horizontally oriented injection sleeve 11 is disposed in a fixed die plate 12 somewhat below its center. The injection sleeve has a feed slot 13 defined centrally in a lower wall portion inserted in the fixed die plate 12. The fixed die plate 12 has an L-shaped pipe hole 14 defined therein beneath the feed slot 13 and in communication therewith. A feed pipe 15 for feeding molten metal into the injection sleeve 11 has one end extending into the pipe hole 14 and coupled to the feed slot 13.
The other end of the feed pipe 15 is joined to a lower portion of a crucible furnace 16 which stores molten metal 17 and keeps the same at a prescribed temperature. An electromagnetic pump 18 is disposed on the feed pipe 15 for feeding the molten metal 17 from the crucible furnace 18 into the injection sleeve 11 and through the feed slot 13. The crucible furnace 16 has a heater 19 for keeping the molten metal 17 in the crucible furnace 16 at a prescribed temperature.
A die cavity 20 is defined by and between a fixed die 21 and a movable die 22. A sensor 23, such as a temperature sensor, may be disposed at the lower end of the die cavity 20 which communicates with the injection sleeve 11 through a runner 24. When a sufficient amount of molten metal is charged in the injection sleeve 11, the sensor 23 contacts the charged molten metal and detects that the dosage supplied to the injection sleeve is enough, i.e. that the injection sleeve is 100% full.
A frame 25 is connected to an outer side surface of the fixed die plate 12 and secured by bolts 26 and tie bars 27 to a movable die plate 28. A rod 29 connected to a coupling 30 and holding an injection plunger tip 31 is connected to the shaft 32 of a hydraulically operated cylinder 33.
Operation of the casting apparatus shown in FIG. 1 shall now be described. The molten metal 17 stored in the crucible furnace 16 is heated and kept at a desired temperature by energizing the heater 19. At this time, the injection plunger tip 31 is retracted to the illustrated position by an injection cylinder 33. The electromagnetic pump 18 is now energized to feed the molten metal 17 from the crucible furnace 16 through the feed pipe 15 and into the injection sleeve 11. The electromagnetic pump 18 is energized to charge the molten metal 17 into the injection sleeve 11 until a desired amount of molten metal 17 is contained in the injection sleeve 11, whereupon it is detected by the sensor 23. The sensor 23 can then generate a signal to a control unit (not shown) for instructing the electromagnetic pump to stop feeding molten metal 17 into the injection sleeve 11.
Then, the injection cylinder 33 is operated for advancing the piston rod 29 thereof at a prescribed speed to cause the injection plunger tip 31 to move forwardly at the same speed. Thus, the molten metal 17 charged in the injection sleeve 11 is forced by the plunger tip 31 through the runner 24 and into the die cavity 20. The molten metal in the die cavity 20 is allowed to cool and solidify. After the metal in the die cavity 20 has become solidified, the injection cylinder 33 is actuated to retract the plunger tip 31 away from the die cavity 20, whereupon the movable and fixed dies 21,22 can be separated and the finished casting product can be removed from the die cavity 20.
With the above arrangement, good performance and quality of finished castings can be achieved when the injection sleeve 11 is horizontally disposed as shown in FIG. 1. However, it sometimes is necessary that the injection sleeve should be vertically oriented for supplying molten metal upwardly to a die cavity situated above the injection sleeve. Conventional arrangements for supplying molten metal upwardly to a die cavity through a vertically oriented injection sleeve are described in FIGS. 2 and 3.
FIG. 2 illustrates a vertically oriented injection sleeve 34 having a vertically oriented rod 35 and plunger tip 36 located therein for forcing molten metal upwardly to a die assembly (not shown). The injection sleeve 34 includes a feed slot 37 near the lower end thereof for providing a passage for the molten metal 17 into the injection sleeve. the feed slot 37 communicates with a feed pipe 38 through a feed block 39. The other end of the feed pipe 38 is connected to the outlet of a crucible furnace 16 containing molten metal 17 heated to a prescribed temperature.
The feed pipe 38, which is in the shape of a crank, provides a fluid passage for the molten metal 17 from the crucible furnace 16 to the feed block 39 and into the injection sleeve 34 through the feed sot 37. The molten metal is advanced through the feed pipe 38 using an electromagnetic pump 18. A heating coil 40 is also provided on the upper portion of the crank-shaped feed pipe 38 nearest the feed block 39 for keeping the metal in its molten state, since this area is remote from the crucible furnace.
The conventional arrangement, as shown in FIG. 2, suffers from the following disadvantages:
First, when the magnetic pump is activated for filling molten metal into the injection sleeve 39, particularly as the molten metal first enters the injection sleeve 39 in the area of the feed slot 37, a significant air space 41 will be developed above the molten metal 17 inside the upper portion of the crank-shaped feed pipe 38. Such an air space 41 will remain in the feed pipe at least until the molten metal 17 is filled into the injection sleeve 34 just above the uppermost area of the feed slot 37. Due to the horizontal orientation of the upper section of the crank-shaped feed pipe 38, a large area on the surface of the molten metal 17 is exposed to air. Such a large surface area S is therefore easily subjected to oxidation by the air in the feed pipe 38, resulting in inferior castings.
Secondly, as the molten metal 17 enters into the injection sleeve 34 through the feed slot 37, there is a tendency for undulation and waves to develop upon the surface S of the molten metal 17. Such waves W can swell up and trap air within the molten metal 17. If such trapped air becomes introduced into the die cavity, inferior castings, having air cavities and blow holes therein, will be produced.
Thirdly, also as a result of the horizontal orientation of the upper portion of the crank-shaped feed pipe 38, when the plunger tip is raised above the feed slot, as shown by the dashed lines in FIG. 2, any remaining molten metal inside the upper portion of the feed pipe 38 will spill out through the feed slot and fall down through the bottom space in the injection sleeve 34 beneath the plunger tip 36. Such spilled molten metal can then collect and solidify upon other portions of the casting apparatus located beneath the injection sleeve 34, for example, upon the cylinder (not shown) which actuates the rod 35 of the plunger tip 36. Such spilled and solidified metal therefore creates a nuisance which can degrade the performance of the casting apparatus.
Finally, since the crank-shaped feed pipe 38 occupies a significant area between the crucible furnace 16 and the feed block 39, and since the feed pipe 38 is exposed to ambient air within this region, it is necessary to provide a heating coil 40 for keeping the metal in its molten state, particularly in the upper portion of the crank-shaped feed pipe 38. However, even when using such a heating coil 40, it is difficult to adequately maintain all of the metal in its molten state within the entire volume of the feed pipe 38. More specifically, the molten metal within the feed pipe 38 has a tendency to solidify on the inside walls of the feed pipe 38 and feed block 39, particularly within the corners of the bent portions of the crank-shaped feed pipe 38 and also within the feed block 39, since these areas are remote from the effective area of the heating coil 40. The solidified metal thus reduces the effective volume of the feed pipe 38 and feed block 39. Since the dosage of molten metal supplied to the injection sleeve is typically controlled dependent upon a known volume inside the feed pipe 38, such reductions in volume within the feed pipe 38 and feed block 39 create problems for accurately controlling the amount of molten metal supplied to the injection sleeve 34. Furthermore, if a portion of the molten metal intended for delivery to the injection sleeve becomes solidified on the walls of the feed pipe during transit between the crucible furnace 16 and the injection sleeve 34, a diminished amount of molten metal will actually be supplied to the feed pipe 38 and die assembly 42, thus resulting in yet another source of error in controlling the dosage of molten metal supplied to the injection sleeve 34 and ultimately to the die cavity.
One attempt to remedy the problems associated with spillage of the molten metal through the bottom portion of the injection sleeve 34 is shown in FIG. 3. In FIG. 3, the same elements which have already been described in relation to the earlier figures shall be denoted by like reference numerals. In this known embodiment, the upper portion of the feed pipe 38 is inclined for providing a sloped passage for the molten metal through the upper portion of the feed pipe 38, through the feed block 39 and feed slot 37 and into the injection sleeve 34. The feed block 39 is also provided with an inclined passage 39a therein. Due to the inclination of the passage through the feed pipe 38 and feed block 39, there is less of a tendency for the molten metal to spill out of the feed passage and through the bottom end of the injection sleeve when the plunger tip 31 is advanced above the feed slot 37. Rather, most of the remaining molten metal in the upper area of the feed block 39 will simply flow back down the inclined passage of the feed block 39 and feed pipe 38 instead of spilling into the bottom end of the injection sleeve 34 through the feed slot 37. However, the arrangement shown in FIG. 3 still suffers from the problems of solidified metal adhering to the walls of the feed pipe 38 and feed block 39 and also from exposure of the surface of the molten metal to a large air space within the feed pipe 38, resulting in unwanted oxidation of the molten metal.